The Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard specification defines the physical (PHY) layer and Media Access Control (MAC) layer for Wireless Local Area Networks (WLANs), cf. IEEE Standard for Information technology—Tele-communications and information exchange between systems. Local and metropolitan area networks—Specific requirements. Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications. According to the Wi-Fi Alliance, a Wi-Fi may be defined as any WLAN products that are based on the Institute of Electrical and Electronics Engineers' (IEEE) 802.11 standards. Thus, in this document the terms Wi-Fi and WLAN will be used interchangeably.
WLAN is based on a technology that currently mainly operates on the 2.4 GHz or the 5 GHz band. The IEEE 802.11 specifications regulate the physical layer, MAC layer and other aspects of one or more access points and mobile terminals comprised in the WLAN in order to secure compatibility and inter-operability between access points and mobile terminals. The mobile terminal is herein sometimes also referred to as a User Equipment (UE). The WLAN is generally operated in unlicensed bands, and as such, communication in the WLAN may be subject to interference sources from any number of both known and unknown devices. The WLAN may be used as a wireless extension to fixed broadband access. For example, this may be the case in domestic environments and hotspots, like airports, train stations and restaurants.
The WLAN technology relies on Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA) in order to effectively and fairly share the wireless medium among different WLAN entities and even among different Radio Access Technologies (RATs). CSMA/CA applied by the WLAN system demands that a node, e.g. an access point or a station, that wishes to send data senses the common communication channel before carrying out a transmission in order to avoid duplicate transmissions on the common communication channel. The reason or this is that duplicate transmission on the common communication channel usually results in loss of data and the need of retransmissions. In order for a node to deem the channel busy, it has to detect a transmission, the received signal strength level of which surpasses a pre-determined threshold, referred to as the Clear Channel Assessment (CCA) Threshold (CCAT). An exemplary relation between the coverage area of a Basic Service Set (BSS) and the CCAT is schematically depicted in FIG. 1.
In current systems, one common CCAT is defined for all nodes operating in the WLAN and this common CCAT is to be used by all nodes when they perform channel sensing for transmission to and from any other node in the WLAN.
FIG. 2 schematically illustrates a WLAN protocol stack. As illustrated, the IEEE layer specification comprises a Data Link Layer comprising a Medium Access Control (MAC) sublayer, and a Physical Layer comprising a Physical Layer Convergence Procedure (PLCP) sublayer and a Physical Medium Dependent (PMD) sublayer. The PLCP sublayer performs the CCA and reports the results to the MAC layer, therefore the CCA threshold is set in the PLCP sublayer.
US 2014/0286203 A1 discloses a wireless communication device that includes communication interface configured to receive and transmit signals and a processor configured to generate and process such signals. The communication interface of the wireless communication device is configured to receive a first signal from a first other wireless communication device, and the processor of the wireless communication device is configured to process the first signal to determine one or more concurrent transmission parameters. The processor of the wireless communication device is configured to generate the second signal based on the one or more concurrent transmission parameters and direct the communication interface to transmit the second signal to a second other wireless communication device during receipt of the first signal from the first other wireless communication device. The wireless communication device may be configured to make such concurrent transmissions based on one or more considerations such as the power level of the first signal.
The state of the art WLANs are associated with some drawbacks such as the suboptimal usage of the transmission medium.